Injection molding is a process in which a molding machine forces melted plastic through a nozzle into a mold cavity where it is held until it solidifies, resulting in a solid part that assumes the shape defined by the cavity. Before injection into the mold, the plastic must be heated to a temperature which allows it to flow under pressure. Molding machines may use a nozzle adapter that defines a melt passage to convey molten plastic from the machine through the nozzle to the mold. It is important to keep the molten material at the proper temperature to optimize the flow of the material into the mold. To achieve and maintain the proper temperature of the material injected into the mold, one or more heaters may be used to heat the nozzle adapter. Currently available nozzle adapters often contain one or more electrically powered cartridge heaters located parallel to the melt passage. In such conventional configurations a cartridge heater is commonly inserted into a circular hole accessed through an end of the nozzle adapter.
For best heater efficiency it is desirable for the outside diameter of the heater to closely match the diameter of the hole into which the heater is inserted. For this reason, it is common to ream the hole to achieve close dimensional tolerances. The conventional method of inserting the heater into a hole requires that the hole diameter be large enough to accommodate a slip fit, which may result in reduced heater efficiency. In the event a heater needs to be replaced, material galling or sticking may make it difficult to extract a heater from a tight cylindrical passageway. It may be necessary to drill out a defective heater from a nozzle adapter, resulting in the potential of damaging the nozzle adapter. For example, the process of drilling out a cartridge heater may result in enlargement of the hole, so that heat transfer between the nozzle adapter and the replacement heater is degraded.
In the conventional configuration described above it is necessary to be able to access the nozzle adapter from its end in order to replace a heater. In a typical injection molding machine, accessibility of the ends of a nozzle adapter requires complete removal of the nozzle adapter from the molding machine. This process is time consuming and may lead to extended machine downtime.
There is a need for an apparatus to contain cartridge heaters in a nozzle adapter that facilitates simplified, more convenient, and reliable replacement of one or more heaters with reduced machine downtime and reduced risk of damaging other components.